Myself and another shadow priest were scratching our heads a bit at how other shadow priests can be putting out <1400 dps on this encounter. Even with both of us soaking we were putting out 1500 each, with suboptimal t6 (missing some spinels, trinkets.) Soaking really doesn't have that much of an adverse effect, SW:D is completely safe as long as you aren't burning, and pay attention to the slash timer. The pushback is spread out enough that it doesn't seriously impact your dps also (unlike say, RoS, P2 Illidan.)
Relevant 6 minute WWS (try to ignore the lack of other dps optimization here)
Note that no destruction pots were used. The only group optimization we had was wrath of air, iirc. Haste and Timbal's seem to be pretty significant gains overall.